Method and device for treating a substrate

ABSTRACT

The invention relates to a method and device for treating a substrate ( 20 ) in an arc vaporization device ( 10 ). An arc current of intensity I flows in an evacuated space ( 12 ) in the arc vaporization device between an anode and a metal target ( 14, 16, 18 ) which acts as a cathode. Said arc current is used to vaporize the target material and produce a metal ion density. The invention aims to treat the substrate ( 20 ) without causing undesirable heating thereof. As a result, the metal ion density per target ( 14, 16, 18 ) is set by at least partially covering the target, said density being effective for treating substrates.

[0001] The invention relates to a method for treating such as etching a substrate in an arc evaporation device in which an arc current of an intensity I flows in an evacuated space between an anode and a target comprising metal and acting as a cathode in order to evaporate target material and generate a metal ion density. The invention further relates to a device for treating such as etching a substrate in an arc evaporation device and comprising a vacuum chamber with an anode and with at least one cathode formed by a target of metal.

[0002] In order to apply coatings, in particular carbide coatings, to materials such as workpieces, it is necessary that the surfaces to be coated are free of impurities on the atomic scale in order to permit firm adhesion of the material to be applied.

[0003] The application of the coatings can be achieved for example by sputtering in a vacuum chamber at a voltage in the range between 400 V and 1500 V and at a current intensity between 1 A and 10 A. If arc technology is used, a voltage of 20 V is typically applied between anode and cathode during the flow of a current in the order of size of 100 A.

[0004] An arc evaporation device is known from EP 0 306 491 B1. In order to apply an alloy coating to a component, a target is used that has at least two different metals in differing active surface sections of the target.

[0005] In order for an arc spot to be moved on a random path over the entire surface of a target in order to evaporate metal and hence generate a plasma, DE 42 43 592 A1 provides for a current to be supplied to the target via a magnetic coil which in turn generates the magnetic field necessary for moving the arc spot.

[0006] During pretreatment of the substrate to be coated such as a tool, i.e. during etching, it is found that on account of the high metal ion density per cathode occurring with a stable arc current unwelcome effects take place, such as excessive beating up of the substrate (tool) and a concomitant loss of hardness in the basic material of the substrate and changes in the geometry of the substrate or application of evaporated material due to atoms and atomic unions (droplets) emitted by the target material, resulting in a poor adhesion of a coating then applied and also in a roughening of the substrate.

[0007] The problem underlying the present invention is to develop a method and a device of the type described at the outset such that treatment such as etching of the substrate is achieved to the necessary extent without the occurrence of any inadmissible heating up. Furthermore, the possibility should be provided that disturbing molecules (residual gas atoms) can be removed very quickly by the treatment of the substrate. Finally, it should then be assured that parasitic deposits on unused targets are ruled out if several targets are present in the arc evaporation device.

[0008] The problem is solved substantially by a method of the type described at the outset in that the metal ion density per target effective for the treatment of the substrate is achieved by at least partial covering of the target. In particular, the metal ion density per target is changed such that an apparent arc current intensity reduction is achieved to a value at which an unstable arc current flows between the anode and the cathode in the normal case.

[0009] In accordance with the invention, the metal ion density per target effective for the substrate to be treated is influenced such that it is reduced to an extent that no inadmissible healing up of the substrate occurs when the arc between anode and target remains stable. In other words, there is an apparent reduction of the current intensity of the arc towards values at which a linear arc source no longer has, at a vacuum in the range of ≦0.0001 millibars, for example, any per se stable operating conditions, i.e. at currents below around 60 A (for typical rectangular evaporators).

[0010] The metal ion densities per target corresponding to low current intensities now become effective for the substrate, so that the required treatment such as etching takes place without the risk of any substrate change or deformation occurring. Here the metal ion density per target can be varied by covering the target on the substrate side to the required extent using at least one cover in the form of, for example, a swivelling flap. In particular, the target is covered on the substrate side by two swivelling flaps.

[0011] Alternatively, the target can be covered on the substrate side using elements having openings adjustable and movable relative to each other, where the openings can be aligned to the required extent flush or offset to one another by adjustment of the elements. This possibility also permits adjustment of the metal ion density per target that is effective for the substrate.

[0012] In an embodiment of the invention, it is provided that the plasma forming between the target and the cover is used for binding gas molecules on the target-side surface of the cover, i.e. is used as a getter pump, hence providing a getter pump with a high pumping capacity. Measurements have indicated that a pumping capacity of 10,000 litres per second is achieved at 100 A per target and with a total of 4 active targets, which in turn can comprise titanium or chromium or another target material with getter effect.

[0013] These getter pumps formed when targets are covered have pumping capacities that are considerably higher than the actual pumping capacity of the turbo pump integrated into the arc evaporation device, which pump usually has a capacity of 500 to 1,000 litres per second. Here the pumping capacity of the getter pumps formed in accordance with the invention are especially effective in particular when the substrate is etched. This prevents the accumulation of gas molecules in the surface of the substrate to be treated, which would have a detrimental effect on the required adhesion effect of the surface.

[0014] The effect of the plasma forming between the target(s) and the covers sealing it/them on the substrate side furthermore results in the advantage that the actual treatment such as etching process can be started earlier than in standard arc evaporation devices working solely with conventional separate pumps. Comparative measurements have shown that the time can easily be shortened by one third with the teachings in accordance with the invention. Normally the heating up of the substrates is faster than the gas emissions in the interior of the chamber.

[0015] A further advantage of the teachings in accordance with the invention can be seen in that unused targets are protected from parasitic depositions during heating up of the substrates to be treated or during deposition with only one cathode by these targets being completely covered. As a result, no additional cleaning processes are required for possibly contaminated targets.

[0016] However, there are also advantages when the substrate is coated, since during coating of the substrate with titanium nitride for example when a target of titanium is used and when nitrogen is supplied, a coating can be applied using the target covers in a controlled way such that very precise and thin coatings can be built up even in the nano layer range. It is also possible to provide multi-layer coatings that can if required be of differing materials, provided the targets used themselves comprise differing materials.

[0017] Further advantages achievable thanks to the teachings in accordance with the invention can be given. Instead of switching off an arc, it can be “concealed” so that there is no plasma interruption. This results in a better coating quality. Also, etching with an inert gas such as argon is possible at pressures in the 10⁻³ mbar range. The inert gas etching otherwise not possible has a very even and gentle effect—thanks to very low ion flows—on the substrates. With the prior art, very expensive ionisation aids would have to be installed. In other words, inert gas ion etching is possible with a simultaneous getter pump effect.

[0018] A device of the type mentioned at the outset is characterised in that the target is coverable on the substrate side to the required extent by a cover. Here the cover can be designed as a single-wing or multiple-wing, in particular as a double-wing flap. It is also possible to surround the target with a perforated sheet element or by two perforated sheet elements adjustable relative to one another in order to cover or expose to the required extent holes present in the perforated sheets.

[0019] Further details, advantages and features of the invention are shown not only in the claims and in the features they contain—singly and/or in combination—but also in the following description of preferred embodiments shown in the drawing.

[0020] In the drawing,

[0021]FIG. 1 shows a principle view of a vacuum chamber of an arc evaporation device,

[0022]FIG. 2 shows a principle view of the extent of a plasma acting on a substrate through a cover assigned to a target and

[0023]FIG. 3 shows a graphic relating to the metal ion density generated in an arc evaporation device as a function of the arc current.

[0024]FIG. 1 shows purely in principle an arc evaporation device 10 that has a vacuum chamber 12 with targets 14, 16, 18 arranged therein and performing the function of cathodes. Substrates 20 are arranged for example on a turntable in the interior of the vacuum chamber 12 and are following the teachings in accordance with the invention, to be at least etched, in particular however initially etched and then coated. A plasma necessary to do so is generated by evaporation of the target material and by formation of an arc current between the cathode/target 14 and/or 16 and/or 18 on the one hand and the anode connected to the evaporation chamber 12 or its wall 24 on the other hand. To that extent however, reference is made to adequately known designs and technologies, similarly with regard to the voltage to be applied, which can be in the order of size of 20 V, and to the flowing current in the order of size of 100 A. The pressure in the arc chamber 12 is rated as a function of the plasma formed or of the etching/coating process and is in the range between 10⁻⁴ and 10³ Pa, these values being only examples.

[0025] Using voltage sources 22 a, 22 b, 22 c assigned to the individual targets 14, 16, 18, the latter have voltage applied to them individually or in a required combination.

[0026] It is now provided in accordance with the invention that the targets 14, 16, 18 are coverable to the required extent relative to the substrate 20, as a result of which the metal ion density per target 14. 16, 18 is variable to an extent that no unwelcome overheating of the substrates 18 occurs during etching, regardless of a stable arc current and hence the formation of an arc spot on the surface of the evaporating target 14, 16, 18.

[0027] This ensures that the surface of the substrates 20 is cleaned to the required extent in order to then apply metal coatings such as carbide coatings with good adhesion.

[0028] In the embodiment, the covers 26, 28, 30 are double-wing flaps 32, 34, which depending on their position relative to one another completely cover the respective target 14, 16, 18 or expose a slot 36 of the required width through which a plasma can form in the direction of the substrates 20. This is made clear in FIG. 2. Here a support 38 for a target 40 is shown purely in principle that on the surface side can be covered by flaps 42, 44, also referred to as shutters, in the direction of a substrate, not shown.

[0029] In representation 1 in FIG. 2, the flaps 42, 44 are completely closed, so that a plasma for example of titanium ions cannot form in the direction of the substrate.

[0030] In position 2, the flaps 42, 44 have an opening slot 46 to one another that enables a plasma 48 to exit in the direction of the substrate. The extent of the plasma and hence the metal ion density varies as a function of the gap width between the flaps 42, 44, as made clear by the further representations 3 and 4 in FIG. 2. The metal ion density released from the target 14 can therefore be varied to the required extent by the setting of the flaps 42, 44, with the result that the metal ion density impacting the substrate can be altered such that during the cleaning process, i.e. during etching, there is no unwelcome overheating.

[0031] However, during coating with metal coatings such as titanium nitride too the flaps 42, 44 have the advantage that thin coatings or several coating layers can be selectively applied to the substrates 20, where these coatings can themselves comprise different materials, i.e. when the vacuum chamber 12 contains targets of differing materials that generate a plasma effective for the substrate to match the required coating sequence.

[0032] The effect of the covers 26, 28, 30, i.e. of flaps 32, 34 or 42, 44, is such that an apparent reduction of the arc current takes place such that a required reduction of the metal ion density per target/cathode is achieved. The metal ion density per cathode effective for the substrate 20 can be reduced by means of the cover 26, 28, 30 as much as if the arc current had been reduced to values with which a stable arc is no longer achievable per se, i.e. in the range of 60 A or less at a pressure in the vacuum chamber 12 of 0.0001 mbar or less.

[0033] This range is identified in FIG. 3 with the reference number 50. In other words, an apparent arc current reduction takes place which however does not lead to any instability of the arc itself. This results also in advantages during low-temperature coating.

[0034] The possibility of completely covering the cathode/targets 14, 16, 18 offers a further advantage. In the case of an arc forming on a target 14, 16, 18, the function of a getter pump can be obtained when the appropriate target is completely covered. In this case, gas molecules present in the vacuum chamber are, on account of the plasma formed between the target and the cover, bound by the target particles being deposited on the cover, the result being that gas molecules are not accumulated in the surface of the substrate 20 or if so only to a negligible extent. Here a suitably generated getter pump has a pump capacity of, for example, 10,000 litres per second at a current intensity of 100 A per cathode and with a total of 4 active cathodes used. As a result, the etching process proper can be used earlier than in known methods.

[0035] Furthermore, there is the advantage that targets not used can be completely covered, so that parasitic deposition of extraneous substances is ruled out.

[0036] The teachings in accordance with the invention therefore offer in particular the following advantages:

[0037] better surface cleaning.

[0038] better adhesion of metal coatings to be applied,

[0039] shortening of process,

[0040] avoidance of contamination of unused targets,

[0041] formation of coating sequences,

[0042] formation of extremely thin coatings (nano layer coatings),

[0043] efficient inert gas ion etching at low inert gas pressures,

[0044] achievement of better low-temperature coating by reduction of ion density with continuous plasma. 

1. A method for treating such as etching a substrate (20) in an arc evaporation device (10) in which an arc current of an intensity I flows in an evacuated space (12) between an anode and a target (14, 16, 18, 40) comprising metal and acting as a cathode in order to evaporate target material and generate a metal ion density, wherein the metal ion density per target (14, 16, 18, 40) effective for treatment of the substrate (20) is achieved by at least partial covering of the target.
 2. Method according to claim 1, wherein the metal ion density per target (14, 16, 18, 40) is changed such that an apparent arc current intensity reduction is achieved to a value at which an unstable arc current flows between the anode and the cathode.
 3. Method according to claim 1 or claim 2, wherein the metal ion density per target (14, 16, 18, 40) is reduced to an extent such that no inadmissible heating up of the substrate (20) occurs when the arc between anode and target remains stable.
 4. Method according to at least one of the previous claims, wherein the target (14, 16, 18, 40) is covered on the substrate side to the required extent by at least one cover (26, 28, 30) preferably in the form of a swivellable flap (32, 34, 42, 44).
 5. Method according to at least one of the previous claims, wherein the target (14, 16, 18, 40) is covered on the substrate side to the required extent by two swivellable flaps (32, 34, 42, 44).
 6. Method according to at least one of the previous claims, wherein the target (14, 16, 18) is covered on the substrate side using elements having openings adjustable and movable relative to each other, where the openings can be aligned to the required extent flush or offset to one another by adjustment of the elements.
 7. Device for treating such as etching a substrate in an arc evaporation device (10) and comprising a vacuum chamber (12) with an anode and with at least one cathode formed by a target (14, 16,18, 40) of metal, wherein the target (14, 16, 18, 40) is covered on the substrate side to the required extent by a cover (26, 28, 30, 32, 34, 42, 44).
 8. Device according to claim 7, wherein the cover (26, 28, 30) is designed as a single-wing or multiple-wing, in particular as a double-wing flap (32, 34, 42, 44).
 9. Device according to claim 7 or claim
 8. wherein the target (14, 16, 18) is covered on the substrate side using elements having openings adjustable/movable relative to each other, where the openings can be aligned to the required extent flush or offset to one another by adjustment of the elements.
 10. Use of the device with the target (14, 16, 18) covered and subjected to an arc for gettering of gas molecules.
 11. Use of the device for inert gas ion etching. 